The present invention relates to power generation using tides as a marine resource. Tidal power generation, which is a kind of power generation method using natural energy resources and which is under development, generates electricity from the kinetic energy of a tide using a water turbine generator installed at a place with a high-speed tide. Tidal power generation using a tide is included in marine current power generation methods in a broad sense (hereafter, ‘tidal power generation’ and ‘tide’ are referred to as ‘marine current power generation’ and ‘marine current’ in combination) and is classified into a helical type, an HAT (Horizontal Axis Turbine) type, and a VAT (Vertical Axis Turbine) type in accordance with the types of water turbine generators, and also classified into a floating type and a submerged type in accordance with the type of water turbine generator installation.
Tidal power generation generates electricity using the tidal range between the marine currents inside and outside artificial seawalls (reservoirs), but marine current power generation generates electricity generally using a water turbine generator installed in the flow of a natural marine current.
Marine current power generation is similar in principle to wind power generation, but is different in that it operates a turbine using a continuous marine current instead of wind. However, the power/area density is about four times larger in the marine current power generation method, as compared with the power generation method using ocean wind, because the density of seawater is about 840 times larger than that of the air. Hence, the facilities required for the marine current power generation are much smaller than those for the wind power generation for the same output capacity.
The output that can be achieved by marine current power generation is in proportion to the efficiency of a water turbine generator and the cross-sectional area of a marine current flowing through the water turbine generator and is in proportion to the cube of a marine current speed, so a high speed is absolutely advantageous in marine current power generation.
The tidal and marine current energy, which is energy from the attraction among the moon, sun, and earth, is an infinite clean energy source as long as the solar system exists, and is not influenced by weather and seasons due to the periodicity of the ebb and flow. Further, there is an advantage that it is possible to expect output for a long period of time, continuously supply power for a predetermined time, and provide easy connection to a power network. However, there is a disadvantage that power is not continuously generated, and when the power generation site is far from the shore, the initial investment cost is high, for example, due to installation of power transmission lines.
Places where tides are fast such as a narrow strait between an island and the land, that is, places where the average speed of tides is 2 m/s or more at a spring tide have been examined as target areas for marine current power generation. However, though tidal power generation has already been used, marine current power generation is not widely used in a large scale over the world. This is because natural sea areas where marine currents are fast such that marine current power generation is possible are very limited over the world, so it is difficult to find appropriate places for installing water turbine generators. Further, even if the average speed of marine currents is satisfied, the speed of marine currents may not be uniform, depending on the submarine topography of the area where a marine current power plant is constructed, and when the flow direction of marine currents is not fixed, it is difficult to ensure structural stability of a water turbine generator and control the amount of power generation with high reliability.
In general, in normal marine current power plants, the average speed of marine currents is 2˜2.5 m/s, the flow direction of marine currents frequently changes, and power generation is much influenced by the topography. However, marine currents that can be obtained in a tidal power plant have more uniform and available kinetic energy than natural marine currents. Actually, it has been reported from Siwha Lake Tidal Power Station (South Korea) that is a one-way rising tidal type that the average speed of water discharged to the lake through a water turbine generator was 3 m/s or more when power is generated using a tidal range of 6 m at high tide, and the average speed of seawater that was sluiced at a tidal range of 1.9 m was 6.0 m/s at low tide.
It is very difficult to achieve normal hydroelectric power generation with those various conditions satisfied, so hydroelectric power generation is not actually widely used. However, at present, studies for conveniently applying hydroelectric power generation to various places where there are various tidal differences are conducted and it is necessary to apply the hydroelectric power generation at this point.